It is known to measure a rotation angle and a rotation speed (angular speed) of a rotating machine (motor, etc.) using a rotation measuring instrument, such as a resolver. The measured rotation angle and rotation speed are used for servo control of a rotating machine.
The resolver outputs a signal obtained by modulating the amplitude of a reference signal supplied from a sine wave oscillator in accordance with the rotation angle of its rotor. The rotor of the resolver and that of the motor share a shaft and it is possible to measure the rotation angle of the motor based on the output signal of the resolver. In the following explanation, an example in which a resolver is used is explained; however, it is possible to apply the present invention to any rotation measuring instrument capable of measuring the rotation angle and rotation speed of a rotating machine (motor, etc.) and not limited to the resolver. Further, explanation is given by taking a motor as an example of the rotating machine.
The angle detection device including a resolver is used for servo control of a motor and is required to have high reliability as well as being capable of detection with high accuracy. An angle detection device having redundancy, in which dual detection is implemented by providing two resolvers configured to detect the rotation of the same motor has been proposed in order to improve reliability. In order to further improve reliability, it can also be considered to provide three or more resolvers configured to detect the rotation of the same motor and the present invention can also be applied to such a case; however, in the following explanation, an example in which two resolvers are provided is explained.
In the angle detection device made redundant, each resolver is provided with an anomaly detection unit configured to monitor an internal signal and to detect the occurrence of an anomaly and whether each resolver is normal is detected. At this time, there is a case where signals of the two resolvers are further compared to find a difference to improve the detection accuracy of the occurrence of an anomaly. Normally, the angle detection device made redundant outputs a rotation angle and a rotation speed measured by one of the resolvers (first resolver). Then, when it is detected that an anomaly has occurred in the first resolver and if the other resolver (second resolver) is normal, switching is performed so that the rotation angle and rotation speed measured by the second resolver are output.
In the case where outputs of the two resolvers are switched, it is considered to simply change the output of the first resolver in which an anomaly has occurred to the output of the normal second resolver. However, during the period from the occurrence of an anomaly in the resolver until the anomaly is detected, the difference between the output of the resolver in which the anomaly has occurred and the output of the normal resolver increases. Because of this, if the output of the first resolver is switched simply to the output of the second resolver, the change in the output of the angle detection device becomes large and there arises a case where a malfunction of the motor control system, such as step-out of the motor, may occur.